It used to be a simple process. A contractor ordered the concrete. A producer delivered the mix. The contractor placed the concrete. A short time later, after the concrete was tested to determine it attained its designed strength, the contractor paid the bill.

But in the last few years, there's been an additional timing element added to the simple month-long process. Now, on many slabs on grade, the concrete doesn't only have to be strong enough, it needs to be dry enough.

Excess moisture wreaks havoc on floor-coating adhesives, blisters epoxy-based coatings, and fosters microbial growth. The subject of improper floor drying is the single largest reason for non-payment by the owner.

While the contractor and design engineer are typically the main parties involved in a potential legal battle, producers should verse their quality-control staff in the current methods of moisture testing.

The preferred method for testing floor dryness has changed in the last few years. Howard Kanare, senior principal scientist at CTLGroup, says the popular anhydrous calcium chloride test used to gauge moisture vapor emission rates on the surface relied upon since the 1940s is not only outdated—it's also inaccurate.

For a quick estimate, manufacturers have developed pin and other test methods. These procedures should only be used as general guidelines, possibly for rapid and preliminary results before more accurate moisture tests.

Most floor experts agree that the relative humidity (RH) testing method offers greater accuracy and precision. As a result, ASTM F-2170, which spells out the issues surrounding RH testing, has become the preferred standard of moisture-testing concrete humidity.

Producers who wish to be proactive in measuring a floor's dryness, should consider these types of testing devices. Circle the appropriate reader service number.

Long-term testing

Developed in partnership with CTL-Group, the rugged, low-cost RapidRH combines a sensor, power supply, and display for testing the relative humidity of a slab from the inside, a method more accurate and effective than surface testing. Install it in new concrete or in existing slabs by drilling a hole. Leave the sensor in the concrete and read with the removable RapidRH reader. The sensor's rugged construction guards against damage during construction or normal use. Wagner Electronics. 800-585-7609. www.rapidrh.com.

RH loggers

IntelliRock loggers measure, log, and monitor moisture conditions in a slab. Drill a hole, place a plastic sleeve, and insert the logger to read the relative humidity of concrete, or monitor moisture levels over time. Operators log humidity information with the software or export to other applications for reporting. Engius Inc. 866-636-4487. www.engius.com.